U.S. patent application number 13/480583 was filed with the patent office on 2012-11-29 for control apparatus for internal combustion engine.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Hideaki ICHIHARA, Hiroshi KATSURAHARA, Keitarou MINAMI, Hiroyuki TAKEZOE.
Application Number | 20120303247 13/480583 |
Document ID | / |
Family ID | 47196838 |
Filed Date | 2012-11-29 |
United States Patent
Application |
20120303247 |
Kind Code |
A1 |
MINAMI; Keitarou ; et
al. |
November 29, 2012 |
CONTROL APPARATUS FOR INTERNAL COMBUSTION ENGINE
Abstract
A cylinder-inflow EGR gas quantity determining arrangement
estimates or senses a value of a cylinder-inflow EGR gas quantity,
which is a quantity of EGR gas that flows into a cylinder of an
internal combustion engine. A misfire predicting arrangement
predicts whether misfire occurs based on the value of the
cylinder-inflow EGR gas quantity and an operational state of the
internal combustion engine. A misfire-avoidance control arrangement
executes at least one misfire-avoidance control operation to avoid
the misfire when the misfire predicting arrangement predicts that
the misfire occurs.
Inventors: |
MINAMI; Keitarou;
(Kariya-city, JP) ; ICHIHARA; Hideaki; (Obu-city,
JP) ; TAKEZOE; Hiroyuki; (Kariya-city, JP) ;
KATSURAHARA; Hiroshi; (Okazaki-city, JP) |
Assignee: |
DENSO CORPORATION
Kariya-city
JP
|
Family ID: |
47196838 |
Appl. No.: |
13/480583 |
Filed: |
May 25, 2012 |
Current U.S.
Class: |
701/104 ;
701/102 |
Current CPC
Class: |
Y02T 10/47 20130101;
G01M 15/11 20130101; F02D 2200/1015 20130101; Y02T 10/40 20130101;
F02D 41/0052 20130101; F02D 41/0072 20130101; F02D 41/1497
20130101 |
Class at
Publication: |
701/104 ;
701/102 |
International
Class: |
F02D 41/26 20060101
F02D041/26; F02B 47/08 20060101 F02B047/08; F02D 41/30 20060101
F02D041/30 |
Foreign Application Data
Date |
Code |
Application Number |
May 27, 2011 |
JP |
2011-119727 |
Apr 2, 2012 |
JP |
2012-83690 |
Claims
1. A control apparatus for an internal combustion engine that is
provided with an exhaust gas recirculation (EGR) device, which
recirculates a portion of exhaust gas of the internal combustion
engine as EGR gas to an intake passage of the internal combustion
engine, the control apparatus comprising: a cylinder-inflow EGR gas
quantity determining arrangement that estimates or senses a value
of a cylinder-inflow EGR gas quantity, which is a quantity of the
EGR gas that flows into a cylinder of the internal combustion
engine; a misfire predicting arrangement that predicts whether
misfire occurs based on the value of the cylinder-inflow EGR gas
quantity and an operational state of the internal combustion
engine; and a misfire-avoidance control arrangement that executes
at least one misfire-avoidance control operation to avoid the
misfire when the misfire predicting arrangement predicts that the
misfire occurs.
2. The control apparatus according to claim 1, further comprising
an upper limit inflow EGR gas quantity computing arrangement that
computes an upper limit inflow EGR gas quantity based on the
operational state of the internal combustion engine, wherein the
upper limit inflow EGR gas quantity is an upper limit of the
cylinder-inflow EGR gas quantity of the EGR gas that is combustible
in the cylinder without causing the misfire, and the misfire
predicting arrangement predicts whether the misfire occurs by
comparing the value of the cylinder-inflow EGR gas quantity with
the upper limit inflow EGR gas quantity.
3. The control apparatus according to claim 2, wherein: the
misfire-avoidance control arrangement computes a required increase
of the upper limit inflow EGR gas quantity, which is required to
avoid the misfire, based on a difference between the value of the
cylinder-inflow EGR gas quantity and the upper limit inflow EGR gas
quantity; and the misfire-avoidance control arrangement executes
the at least one misfire-avoidance control operation under a
corresponding condition, which corresponds to the required increase
of the upper limit inflow EGR gas quantity.
4. The control apparatus according to claim 3, wherein the
misfire-avoidance control arrangement selects the at least one
misfire-avoidance control operation from a plurality of
misfire-avoidance control operations in view of at least one of
fuel economy, driveability, engine responsiveness and engine
emission when the misfire-avoidance control arrangement executes
the at least one misfire-avoidance control operation under the
corresponding condition, which corresponds to the required increase
of the upper limit inflow EGR gas quantity.
5. The control apparatus according to claim 1, wherein the
misfire-avoidance control arrangement executes the at least one
misfire-avoidance control operation, which is selected from: a fuel
injection quantity increasing control operation, which increases a
fuel injection quantity of fuel to be supplied into the cylinder;
an ignition energy increasing control operation, which increases an
ignition energy for igniting the fuel; a gas flow strengthening
control operation, which strengthens a gas flow in the cylinder;
and an intake air quantity increasing control operation, which
increases an intake air quantity of intake air to be supplied into
the cylinder.
6. The control apparatus according to claim 5, wherein when the
misfire-avoidance control arrangement executes the intake air
quantity increasing control operation as one of the at least one
misfire-avoidance control operation, the misfire-avoidance control
arrangement executes a torque correcting control operation, which
limits a torque change that is caused by the intake air quantity
increasing control operation.
7. The control apparatus according to claim 1, wherein: the
cylinder-inflow EGR gas quantity determining arrangement estimates
the value of the cylinder-inflow EGR gas quantity based on an EGR
valve-passing gas flow quantity, which is a quantity of a portion
of the EGR gas that passes through an EGR valve of the EGR device;
and the misfire predicting arrangement compares the estimated value
of the cylinder-inflow EGR gas quantity with an upper limit inflow
EGR gas quantity to predict whether the misfire occurs in advance
before the portion of the EGR gas, which corresponds to the
estimated value of the cylinder-inflow EGR gas quantity, flows into
the cylinder to provide an execution time period to the
misfire-avoidance control arrangement for executing the at least
one misfire-avoidance control operation before the portion of the
EGR gas flows into the cylinder in a case where the misfire
predicting arrangement predicts that the misfire occurs.
8. The control apparatus according to claim 1, wherein: the
cylinder-inflow EGR gas quantity determining arrangement estimates
and stores a value of an EGR gas flow quantity of a portion of the
EGR gas that is present between a first location of the intake
passage, which is on a downstream side of an EGR valve of the EGR
device, and a second location of the intake passage, which is on an
upstream side of the cylinder, based on an EGR valve-passing gas
flow quantity, which is a quantity of the portion of the EGR gas
passed through the EGR valve; and the cylinder-inflow EGR gas
quantity determining arrangement estimates the value of the
cylinder-inflow EGR gas quantity based on the stored value of the
EGR gas flow quantity of the portion of the EGR gas.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese Patent Application No. 2011-119727 filed on May
27, 2011 and Japanese Patent Application No. 2012-83690 filed on
Apr. 2, 2012.
TECHNICAL FIELD
[0002] The present disclosure relates to a control apparatus for an
internal combustion engine provided with an EGR device.
BACKGROUND
[0003] There is known an internal combustion engine of a vehicle,
which is provided with an EGR device to recirculate a portion of
exhaust gas as EGR gas to an intake passage for the purpose of
improving fuel consumption and reducing knocking and exhaust
emissions of the internal combustion engine.
[0004] However, in the internal combustion engine, which is
provided with the EGR device, even when an EGR valve is closed at
the time of driving a throttle valve to a closing side thereof (at
the time of controlling an opening degree of the throttle valve to
a closing side), the EGR gas may remain in a portion of an EGR
passage located on a downstream side of the EGR valve or in the
intake passage in a system. Particularly in a system, which
recirculates the EGR gas to a portion of the intake passage located
on the upstream side of the throttle valve, a large quantity of the
EGR gas may remain in the portion of the intake passage located on
the upstream side of the throttle valve. Therefore, in such a
system, the quantity of the EGR gas, which flows into a cylinder of
the internal combustion engine at the time of decelerating the
engine (thereby decelerating the vehicle) or the time of
reaccelerating the engine (thereby reaccelerating the vehicle), may
be excessively increased to cause a deterioration of a combustion
state, thereby possibly resulting in occurrence of misfire.
[0005] In view of the above point, JP2010-36780A teaches a
technique of limiting combustion deterioration in the internal
combustion engine. Specifically, according to the technique of
JP2010-36780A, a throttle valve is closed at a speed that is slower
than an upper limit valve closing speed, above which the misfire
will likely occur (i.e., the throttle opening degree being reduced
at a speed that is lower than an upper limit closing speed, above
which the misfire will likely occur). In this way, the combustion
deterioration is limited.
[0006] Here, it should be noted that depending on the operational
state immediately before the time of decelerating the engine, a
large quantity of EGR gas may be already present in the intake
passage at the time of starting the deceleration of the engine.
However, technique of JP2010-36780A is a technique that limits the
suctioning of the EGR gas by closing the throttle valve at the
speed, which is lower than the upper limit closing speed of the
throttle valve, and thereby limiting a rapid decrease of the intake
conduit pressure (a rapid increase of an intake conduit negative
pressure). In the case where the large quantity of EGR gas is
already present in the intake passage at the time of starting the
deceleration of the engine, the quantity of the EGR gas, which
flows into the cylinder, becomes excessively large according to
this technique, thereby possibly resulting in misfire. Furthermore,
the above technique cannot counteract with a case where the EGR gas
remains in the intake passage until the time of reaccelerating the
engine after the execution of the deceleration of the engine,
thereby possibly resulting in occurrence of misfire at the time of
reacceleration of the engine.
SUMMARY
[0007] The present disclosure addresses the above
disadvantages.
[0008] According to the present disclosure, there is provided a
control apparatus for an internal combustion engine that is
provided with an exhaust gas recirculation (EGR) device, which
recirculates a portion of exhaust gas of the internal combustion
engine as EGR gas to an intake passage of the internal combustion
engine. The control apparatus includes a cylinder-inflow EGR gas
quantity determining arrangement, a misfire predicting arrangement
and a misfire-avoidance control arrangement. The cylinder-inflow
EGR gas quantity determining arrangement estimates or senses a
value of a cylinder-inflow EGR gas quantity, which is a quantity of
the EGR gas that flows into a cylinder of the internal combustion
engine. The misfire predicting arrangement predicts whether misfire
occurs based on the value of the cylinder-inflow EGR gas quantity
and an operational state of the internal combustion engine. The
misfire-avoidance control arrangement executes at least one
misfire-avoidance control operation to avoid the misfire when the
misfire predicting arrangement predicts that the misfire
occurs.
[0009] The cylinder-inflow EGR gas quantity determining arrangement
may estimate the value of the cylinder-inflow EGR gas quantity
based on an EGR valve-passing gas flow quantity, which is a
quantity of a portion of the EGR gas that passes through an EGR
valve of the EGR device. The misfire predicting arrangement may
compare the estimated value of the cylinder-inflow EGR gas quantity
with an upper limit inflow EGR gas quantity to predict whether the
misfire occurs in advance before the portion of the EGR gas, which
corresponds to the estimated value of the cylinder-inflow EGR gas
quantity, flows into the cylinder to provide an execution time
period to the misfire-avoidance control arrangement for executing
the at least one misfire-avoidance control operation before the
portion of the EGR gas flows into the cylinder in a case where the
misfire predicting arrangement predicts that the misfire
occurs.
[0010] Additionally or alternatively, the cylinder-inflow EGR gas
quantity determining arrangement may estimate and store a value of
an EGR gas flow quantity of a portion of the EGR gas that is
present between a first location of the intake passage, which is on
a downstream side of the EGR valve of the EGR device, and a second
location of the intake passage, which is on an upstream side of the
cylinder, based on an EGR valve-passing gas flow quantity, which is
a quantity of the portion of the EGR gas passed through the EGR
valve. The cylinder-inflow EGR gas quantity determining arrangement
may estimate the value of the cylinder-inflow EGR gas quantity
based on the stored value of the EGR gas flow quantity of the
portion of the EGR gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The drawings described herein are for illustration purposes
only and are not intended to limit the scope of the present
disclosure in any way.
[0012] FIG. 1 is a schematic diagram showing a structure of an
engine control system, which controls an internal combustion engine
provided with a supercharger, according to an embodiment of the
present disclosure;
[0013] FIG. 2 is a diagram showing a time chart for describing
occurrence of misfire caused by EGR gas at the time of decelerating
the engine or the time of reaccelerating the engine;
[0014] FIG. 3 is a flowchart showing a flow of a misfire-avoidance
control routine according to the embodiment;
[0015] FIG. 4 is a flowchart showing a flow of a misfire-avoidance
control execution routine according to the embodiment;
[0016] FIG. 5 is a diagram schematically showing an example of a
misfire-avoidance control operation selection map according to the
embodiment;
[0017] FIG. 6 is a block diagram for describing a computation
method for computing a cylinder-inflow EGR gas quantity according
to the embodiment;
[0018] FIG. 7 is a diagram for describing an EGR valve model
according to the embodiment;
[0019] FIG. 8 is a block diagram for describing an EGR gas delay
model according to the embodiment;
[0020] FIG. 9 is a diagram for describing an intake conduit
advection delay model according to the embodiment;
[0021] FIG. 10A is a diagram showing a change in a throttle opening
degree with time;
[0022] FIG. 10B is a diagram showing a change in the
cylinder-inflow EGR gas quantity and a change in the upper limit
inflow EGR gas quantity with time in a first comparative
example;
[0023] FIG. 10C is a diagram showing a change in the
cylinder-inflow EGR gas quantity and a change in the upper limit
inflow EGR gas quantity with time in a second comparative example;
and
[0024] FIG. 10D is a diagram showing a change in the
cylinder-inflow EGR gas quantity and a change in the upper limit
inflow EGR gas quantity with time according to the embodiment of
the present disclosure.
DETAILED DESCRIPTION
[0025] An embodiment of the present disclosure will be described
with reference to the accompanying drawings.
[0026] First of all, a structure of an engine control system, which
controls an internal combustion engine provided with a
supercharger, will be described with reference to FIG. 1.
[0027] An air cleaner 13 is placed at a furthermost upstream
portion of an intake conduit 12 (an intake passage) of the internal
combustion engine (hereinafter simply referred to as the engine)
11. An air flow meter 14 is placed in the intake conduit 12 on the
downstream side of the air cleaner 13 in a flow direction of the
intake air to sense a flow quantity of the intake air (fresh air).
A catalytic converter (e.g., a three-way catalytic converter) 16 is
placed in an exhaust conduit 15 (an exhaust passage) of the engine
11 to purify the exhaust gas by converting noxious substances, such
as carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx)
of the exhaust gas into less noxious substances.
[0028] An exhaust turbine supercharger 17, which supercharges the
intake air, is provided to the engine 11. An exhaust turbine 18 of
the supercharger 17 is placed on an upstream side of the catalytic
converter 16 in a flow direction of exhaust gas in the exhaust
conduit 15. A compressor 19 of the supercharger 17 is placed on a
downstream side of the air flow meter 14 in the intake conduit 12.
In the supercharger 17, the exhaust turbine 18 and the compressor
19 are coupled with each other to rotate integrally. When the
exhaust turbine 18 is rotated by a kinetic energy of the exhaust
gas, the compressor 19 is rotated to supercharge the intake
air.
[0029] A throttle valve 21 and a throttle opening degree sensor 22
are placed on a downstream side of the compressor 19 in the intake
conduit 12. The throttle valve 21 is driven by an electric motor 20
to adjust an opening degree thereof. The throttle opening degree
sensor 22 senses the opening degree (a throttle opening degree) of
the throttle valve 21.
[0030] An intercooler, which cools the intake air, is provided
integrally with a surge tank 23 (the intake passage) at a location
that is on a downstream side of the throttle valve 21. Here, it
should be noted that the intercooler may be placed on an upstream
side of the surge tank 23 and/or the throttle valve 21, if desired.
An intake manifold 24 (the intake passage), which guides the air
into the respective cylinders of the engine 11, is provided to the
surge tank 23. Furthermore, fuel injection valves (not shown) are
provided for the cylinders such that each fuel injection valve (not
shown) is adapted to inject fuel into the corresponding cylinder or
a corresponding intake port associated with the cylinder. Spark
plugs (not shown) are provided for the cylinders, respectively, and
are installed to a cylinder head of the engine 11. A mixture of
fuel and air in each cylinder is ignited through spark discharge of
the spark plug.
[0031] An exhaust manifold 25 is connected to an exhaust opening of
each cylinder of the engine 11, and a downstream side merging
portion of the exhaust manifold 25 is connected to a portion of the
exhaust conduit 15, which is located on an upstream side of the
exhaust turbine 18. An exhaust gas bypass passage 26 bypasses the
exhaust turbine 18 by connecting between a portion of the exhaust
manifold 25, which is located on an upstream side of the exhaust
turbine 18, and a portion of the exhaust conduit 15, which is
located on a downstream side of the exhaust turbine 18. A wastegate
valve 27 is installed in the exhaust gas bypass passage 26 to open
or close the exhaust gas bypass passage 26.
[0032] A low pressure loop exhaust gas recirculation (LPL EGR)
device 28 is provided to the engine 11. The EGR device 28
recirculates a part of the exhaust gas as EGR gas from the exhaust
conduit 15 into the intake conduit 12. In the EGR device 28, an EGR
conduit 29 (an EGR passage) connects between a portion of the
exhaust conduit 15, which is located on a downstream side of the
catalytic converter 16, and a portion of the intake conduit 12,
which is located on an upstream side of the compressor 19. An EGR
cooler 30 and an EGR valve 31 are provided in the EGR conduit 29.
The EGR cooler 30 cools the EGR gas. The EGR valve 31 adjusts a
flow quantity (EGR gas flow quantity) of the EGR gas, which flows
through the EGR conduit 29. An opening degree of the EGR valve 31
is adjusted by an actuator (not shown), such as an electric motor.
When the EGR valve 31 is opened, the EGR gas is recirculated from
the portion of the exhaust conduit 15, which is located on the
downstream side of the catalytic converter 16, to the portion of
the intake conduit 12, which is located on the upstream side of the
compressor 19.
[0033] Furthermore, an intake side variable valve timing mechanism
32 and an exhaust side variable valve timing mechanism 33 are
provided to the engine 11. The intake side variable valve timing
mechanism 32 adjusts, i.e., changes valve timing (opening timing
and closing timing) of intake valves (not shown). The exhaust side
variable valve timing mechanism 33 adjusts, i.e., changes the valve
timing of exhaust valves (not shown). Furthermore, a coolant
temperature sensor 34 and a crank angle sensor 35 are provided to
the engine 11. The coolant temperature sensor 34 senses the
temperature of engine coolant, which is circulated to cool the
engine 11. The crank angle sensor 35 outputs a pulse signal at
every predetermined crank angle upon rotation of a crankshaft (not
shown). A crank angle and an engine rotational speed are sensed,
i.e., are determined based on the output signals of the crank angle
sensor 35.
[0034] Outputs of the above-described sensors are supplied to an
electronic control unit (ECU) 36. The ECU 36 includes a
microcomputer as its main component. When the ECU 36 executes
engine control programs, which are stored in a ROM (a storage) of
the ECU 36, for example, a fuel injection quantity of each fuel
injection valve, ignition timing of each spark plug and the opening
degree of the throttle valve 21 (an intake air quantity) are
controlled based on the engine operational state.
[0035] At that time, the ECU 36 computes a target EGR rate based on
an engine operational state (e.g., an engine load and the engine
rotational speed) and controls the opening degree of the EGR valve
31 to implement the target EGR rate.
[0036] However, as shown in FIG. 2, in the engine 11, which is
provided with the EGR device 28, even when the EGR valve 31 is
closed at the time of controlling the opening degree of the
throttle valve 21 to the closing side thereof during deceleration
of the engine 11 (deceleration of the vehicle), the EGR gas remains
in the portion of the EGR conduit 29, which is located on the
downstream side of the EGR valve 31, as well as in the intake
conduit 12. Particularly, in the system, which recirculates the EGR
gas to the portion of the intake passage located on the upstream
side of the throttle valve 21, a large quantity of the EGR gas may
remain in the portion of the intake passage located on the upstream
side of the throttle valve 21. Therefore, the quantity of the EGR
gas, which flows into the cylinder at the time of deceleration of
the engine 11 or at the time of reacceleration of the engine 11
after the deceleration, may become excessively large to cause
deterioration of the combustion state of the engine 11, possibly
resulting in misfire.
[0037] According to the present embodiment, the ECU 36 executes
routines for avoiding the misfire shown in FIGS. 3 and 4 as a
countermeasure against the misfire. The ECU 36 estimates a quantity
of the EGR gas supplied into the cylinder (also referred to as a
cylinder-inflow EGR gas quantity) by using an estimating method
(see FIGS. 6 to 9) described later. Furthermore, the ECU 36
computes an upper limit quantity of the cylinder-inflow EGR gas
(hereinafter referred to as an upper limit inflow EGR gas quantity)
based on the engine operational state. The upper limit inflow EGR
gas quantity is an upper limit of the allowable cylinder-inflow EGR
gas quantity, equal to or below which normal combustion (combustion
without misfire) is possible. The ECU 36 compares the
cylinder-inflow EGR gas quantity (the estimated value of the
cylinder-inflow EGR gas quantity) and the upper limit inflow EGR
gas quantity and predicts whether misfire will occur based on this
comparison. When it is predicted that the misfire will occur, the
ECU 36 executes a misfire-avoidance control operation(s) to avoid
the misfire. At that time, the ECU 36 computes a required increase
of the upper limit inflow EGR gas quantity based on a difference
between the cylinder-inflow EGR gas quantity and the upper limit
inflow EGR gas quantity (the currently set upper limit inflow EGR
gas quantity). The required increase of the upper limit inflow EGR
gas quantity is an increase in the upper limit inflow EGR gas
quantity, which needs to be achieved to limit or avoid occurrence
of the misfire. The selected misfire-avoidance control operation(s)
is executed under a condition, which corresponds to the required
increase of the upper limit inflow EGR gas quantity.
[0038] Here, it should be noted that in place of the
cylinder-inflow EGR gas quantity and the corresponding upper limit
inflow EGR gas quantity discussed above, a cylinder-inflow EGR rate
and an upper limit EGR rate indicated below may be used.
Cylinder-Inflow EGR Rate=(Cylinder-inflow EGR Gas Quantity/Total
Cylinder-inflow Gas Quantity)
Upper Limit EGR Rate=(Upper limit inflow EGR gas quantity/Total
Cylinder-inflow Gas Quantity)
[0039] Here, it should be noted that the total cylinder-inflow gas
quantity is a sum of the cylinder-inflow fresh air quantity and the
cylinder-inflow EGR gas quantity.
[0040] Now, the routines of FIGS. 3 and 4, which are executed by
the ECU 36 in the present embodiment, will be described.
[0041] The misfire-avoidance control routine, i.e., the
misfire-avoidance control process of FIG. 3 is executed at a
predetermined cycle during an ON period of the electric power
source of the ECU 36 (a period of turning on of an ignition switch)
and serves as a misfire-avoidance control means. When the present
routine is started, the operation proceeds to step 101. At step
101, engine operational condition parameters (e.g., the engine
rotational speed and the intake air quantity) are obtained.
[0042] Thereafter, the operation proceeds to step 102. At step 102,
a cylinder-inflow EGR gas quantity estimating routine (not shown)
is executed by a cylinder-inflow EGR gas quantity determining
arrangement 36a of the ECU 36 to estimate the cylinder-inflow EGR
gas quantity through the estimating method described later (see
FIGS. 6 to 9). This process at step 102 may serve as a
cylinder-inflow EGR gas quantity determining means.
[0043] Thereafter, the operation proceeds to step 103. At step 103,
the upper limit inflow EGR gas quantity (the upper limit of the
cylinder-inflow EGR gas quantity of the EGR gas, which is normally
combustible without causing misfire in the cylinder) is computed by
an upper limit inflow EGR gas quantity computing arrangement 36d of
the ECU 36 by using a map or a mathematical equation based on the
engine operational state (e.g., the intake air flow quantity). The
map or the equation for determining the upper limit inflow EGR gas
quantity is prepared in advance based on experimental data or
design data and is stored in the ROM of the ECU 36. This process at
step 103 may serve as an upper limit inflow EGR gas quantity
computing means.
[0044] Thereafter, the operation proceeds to step 104. At step 104,
the cylinder-inflow EGR gas quantity is compared with the currently
set upper limit inflow EGR gas quantity, and it is determined
whether the misfire will occur based this comparison. Specifically,
a misfire predicting arrangement 36b of the ECU 36 predicts, i.e.,
determines whether the misfire will occur by determining whether a
value of difference between the currently set upper limit inflow
EGR gas quantity and the cylinder-inflow EGR gas quantity is
smaller than a predetermined threshold value. When the
cylinder-inflow EGR gas quantity exceeds the currently set upper
limit inflow EGR gas quantity, the misfire occurs. Therefore, it is
possible to accurately predict whether the misfire will occur by
determining whether the value of difference between the currently
set upper limit inflow EGR gas quantity and the cylinder-inflow EGR
gas quantity is smaller than the threshold value. This process at
step 104 may serve as a misfire occurrence predicting means.
[0045] In a case where it is determined that the misfire will occur
at step 104 (a case where the value of difference between the
currently set upper limit inflow EGR gas quantity and the
cylinder-inflow EGR gas quantity is smaller than the threshold
value), the operation proceeds to step 105. At step 105, the
required increase of the upper limit inflow EGR gas quantity is
computed by using a map or a mathematical equation based on the
difference between the cylinder-inflow EGR gas quantity and the
currently set upper limit inflow EGR gas quantity (i.e., an excess
of the cylinder-inflow EGR gas quantity relative to the currently
set upper limit inflow EGR gas quantity, thereby serving as
information that indicates a combustion deterioration degree). The
map or the equation for determining the required increase of the
upper limit inflow EGR gas quantity is prepared in advance based on
experimental data or design data and is stored in the ROM of the
ECU 36.
[0046] Alternatively, a value, which is obtained by dividing the
difference between the cylinder-inflow EGR gas quantity and the
upper limit inflow EGR gas quantity (the excess of the
cylinder-inflow EGR gas quantity relative to the upper limit inflow
EGR gas quantity) by the total cylinder-inflow gas quantity, may be
used as the required increase of the upper limit inflow EGR gas
quantity. Further alternatively, in the case where the
cylinder-inflow EGR rate and the upper limit EGR rate are used in
place of the cylinder-inflow EGR gas quantity and the upper limit
inflow EGR gas quantity, the difference between the cylinder-inflow
EGR rate and the upper limit EGR rate (the excess of the
cylinder-inflow EGR rate relative to the limit EGR rate) may be
computed as the required increase of the upper limit inflow EGR gas
quantity.
[0047] Thereafter, the operation proceeds to step 106. At step 106,
the misfire-avoidance control execution routine of FIG. 4 is
executed by a misfire-avoidance control arrangement 36c of the ECU
36 as follows to execute the selected misfire-avoidance control
operation(s) under the condition, which corresponds to the required
increase of the upper limit inflow EGR gas quantity that needs to
be achieved to avoid the misfire.
[0048] First of all, at step 201, a first priority condition is
selected for the present time (present cycle of the routine) from
first to fourth conditions (1) to (4) listed below based on the
current operational state (e.g., the engine rotational speed, the
engine load, the vehicle speed, the accelerator opening degree
and/or a shift position of a shift lever of a transmission) and/or
a currently selected drive mode (e.g., an economy mode, a sports
mode).
[0049] (1) Fuel-economy-oriented Condition
[0050] (2) Driveability-oriented Condition
[0051] (3) Responsiveness-oriented Condition
[0052] (4) Emission-oriented Condition
[0053] When the first priority condition is selected for the
present time (the present cycle of the routine) from the first to
fourth conditions (1) to (4) discussed above at step 201, the
operation proceeds to a corresponding one of steps 202 to 205 based
on the result of the selection made at step 201 (i.e., the selected
one of the first to fourth conditions (1) to (4) discussed above)
to select and execute the corresponding misfire-avoidance control
operation(s), which satisfies the required increase of the upper
limit inflow EGR gas quantity and the first priority condition,
among a plurality of misfire-avoidance control operations by using
a misfire-avoidance control operation selection map shown in FIG.
5. In the misfire-avoidance control operation selection map of FIG.
5, an expected increase of the upper limit inflow EGR gas quantity,
a fuel economy deterioration degree, a drivability deterioration
degree, a responsiveness deterioration degree (more specifically,
an engine responsiveness deterioration degree) and an emission
deterioration degree (more specifically, an engine emission
deterioration degree) are set for each of the misfire-avoidance
control operations (a) to (d). Furthermore, in FIG. 5, the expected
increase of the upper limit EGR gas quantity is indicated by a
concentration (%) of the inflow EGR gas as an example of the inflow
EGR gas quantity. However, the EGR gas quantity may be
alternatively expressed by its weight or volume. The
misfire-avoidance control operation selection map is prepared in
advance based on test data and design data and is prestored in the
ROM of the ECU 36.
[0054] When the first condition, i.e., the fuel-economy-oriented
condition is selected as the first priority condition of the
present time at step 201, the operation proceeds to step 202. At
step 202, in view of the expected increase of the upper limit
inflow EGR gas quantity and the fuel economy deterioration degree
of the respective misfire-avoidance control operations shown in
FIG. 5, a combination (also referred to as a set) of the
misfire-avoidance control operation(s) (at least one of the
misfire-avoidance control operations) is selected such that a sum
of the expected increase(s) of the upper limit inflow EGR gas
quantity of the combination becomes equal to or larger than the
required increase of the upper limit inflow EGR gas quantity, and a
sum of the fuel economy deterioration degree(s) of the combination
becomes minimum. Then, the selected combination (selected set) of
the misfire-avoidance control operation(s) is executed.
[0055] When the second condition, i.e., the driveability-oriented
condition is selected as the first priority condition of the
present time at step 201, the operation proceeds to step 203. At
step 203, in view of the expected increase of the upper limit
inflow EGR gas quantity and the driveability deterioration degree
of the respective misfire-avoidance control operations shown in
FIG. 5, a combination of the misfire-avoidance control operation(s)
(at least one of the misfire-avoidance control operations) is
selected such that a sum of the expected increase(s) of the upper
limit inflow EGR gas quantity of the combination becomes equal to
or larger than the required increase of the upper limit inflow EGR
gas quantity, and a sum of the driveability deterioration degree(s)
of the combination becomes minimum. Then, the selected combination
(selected set) of the misfire-avoidance control operation(s) is
executed.
[0056] When the third condition, i.e., the responsiveness-oriented
condition (i.e., the engine responsiveness oriented condition) is
selected as the first priority condition of the present time at
step 201, the operation proceeds to step 204. At step 204, in view
of the expected increase of the upper limit inflow EGR gas quantity
and the responsiveness deterioration degree of the respective
misfire-avoidance control operations shown in FIG. 5, a combination
of the misfire-avoidance control operation(s) (at least one of the
misfire-avoidance control operations) is selected such that a sum
of the expected increase(s) of the upper limit inflow EGR gas
quantity of the combination becomes equal to or larger than the
required increase of the upper limit inflow EGR gas quantity, and a
sum of the responsiveness deterioration degree(s) of the
combination becomes minimum. Then, the selected combination
(selected set) of the misfire-avoidance control operation(s) is
executed.
[0057] When the fourth condition, i.e., the emission-oriented
condition is selected as the first priority condition of the
present time at step 201, the operation proceeds to step 205. At
step 205 in view of the expected increase of the upper limit inflow
EGR gas quantity and the emission deterioration degree of the
respective misfire-avoidance control operations shown in FIG. 5, a
combination of the misfire-avoidance control operation(s) (at least
one of the misfire-avoidance control operations) is selected such
that a sum of the expected increase(s) of the upper limit inflow
EGR gas quantity of the combination becomes equal to or larger than
the required increase of the upper limit inflow EGR gas quantity,
and a sum of the emission deterioration degree(s) of the
combination becomes minimum. Then, the selected combination
(selected set) of the misfire-avoidance control operation(s) is
executed.
[0058] The selectable misfire-avoidance control operations
discussed above may include the following control operations.
[0059] (I) Fuel Injection Quantity Increasing Control Operation
[0060] The fuel injection quantity increasing control operation is
a control operation that increases the fuel injection quantity of
the fuel injection valve.
[0061] (II) First Ignition Energy Increasing Control Operation
[0062] The first ignition energy increasing control operation is a
control operation that increases the ignition energy of the spark
plug by lengthening a spark discharge time period of the spark
plug.
[0063] (III) Second Ignition Energy Increasing Control
Operation
[0064] The second ignition energy increasing control operation is a
control operation that increases the ignition energy of the spark
plug by increasing an electric current for energizing the spark
plug.
[0065] (IV) Third Ignition Energy Increasing Control Operation
[0066] The third ignition energy increasing control operation is a
control operation that increases the ignition energy of the spark
plug by increasing the number of ignitions of the spark plug.
[0067] (V) First Gas Flow Strengthening Control Operation
[0068] The first gas flow strengthening control operation is a
control operation that strengthens a tumble flow in the cylinder
through a tumble control valve.
[0069] (VI) Second Gas Flow Strengthening Control Operation
[0070] The second gas flow strengthening control operation is a
control operation that strengthens a swirl flow in the cylinder
through a swirl control valve.
[0071] (VII) Third Gas Flow Strengthening Control Operation
[0072] The third gas flow strengthening control operation is a
control operation that strengthens a gas flow by increasing a flow
velocity of the intake air, which flows into the cylinder, through
a reduction in the lift amount of the intake valve that reduces an
open cross-sectional area of the intake passage, which supplies the
intake air into the cylinder.
[0073] (VIII) Fourth Gas Flow Strengthening Control Operation
[0074] The fourth gas flow strengthening control operation is a
control operation that strengthens a gas flow by injecting fresh
air into the cylinder through a fresh air injection valve that is
adapted to inject the fresh air into the cylinder.
[0075] (IX) Intake Air Quantity Increasing Control Operation
[0076] The intake air quantity increasing control operation is a
control operation that increases the intake air quantity by
increasing the throttle opening degree.
[0077] When the fuel injection quantity is increased by the fuel
injection quantity increasing control operation, the ignitability
and the combustion speed of the mixture gas (air-fuel mixture) can
be increased to improve the combustion state, and thereby it is
possible to limit the occurrence of the misfire. Furthermore, when
the ignition energy is increased through the ignition energy
increasing control operation, the ignitability of the mixture gas
is increased to improve the combustion state, and thereby it is
possible to limit the occurrence of the misfire. Furthermore, when
the gas flow is strengthened through the gas flow strengthening
control operation, the combustion speed of the mixture gas is
increased to improve the combustion state, and thereby it is
possible to limit the occurrence of the misfire. Furthermore, when
the intake air quantity is increased through the intake air
quantity increasing control operation, the cylinder-inflow air
quantity is increased to improve the EGR tolerance, and thereby it
is possible to limit the occurrence of the misfire.
[0078] In the routine of FIG. 4, the combination of the
misfire-avoidance control operation(s) is changed according to the
required increase of the upper limit inflow EGR gas quantity.
However, the present disclosure is not limited to this. For
instance, a control quantity (controlled quantity, i.e., controlled
amount) of the misfire-avoidance control operation(s) (e.g., an
increased fuel injection quantity, an increased ignition energy
amount, an increased gas flow strengthening amount, an increased
intake air quantity) or the execution timing of the
misfire-avoidance control operation(s) may be changed according to
the required increase of the upper limit inflow EGR gas
quantity.
[0079] Thereafter, the operation proceeds to step 107 of FIG. 3. At
step 107, in the case where the intake air quantity increasing
control operation is executed (in the case where the intake air
quantity increasing control operation is selected as the
misfire-avoidance control operation), a torque correcting control
operation(s), which limits a torque change (torque increase) of the
engine 11 caused by the intake air quantity increasing control
operation, is executed. In this way, a torque increase of the
engine 11, which is caused by the intake air quantity increasing
control operation, can be absorbed, i.e., counteracted by a torque
decrease, which is caused by the torque correcting control
operation(s), to limit or minimize the torque change caused by the
intake air quantity increasing control operation, and thereby it is
possible to limit the deterioration of the driveability.
[0080] The executable torque correcting control operations
discussed above may include the following control operations.
[0081] (I) Control operation, which reduces the torque of the
engine 11 by stopping an operation of at least one of the
cylinders.
[0082] (II) Control operation, which reduces the torque of the
engine 11 by retarding the ignition timing from the most
appropriate ignition timing, i.e., the minimum advance for the best
torque (MBT) timing.
[0083] (III) Control operation, which reduces the torque of the
engine 11 by generating a brake force through an antilock brake
system (ABS).
[0084] (IV) Control operation, which reduces the torque of the
engine 11 by driving an auxiliary device (e.g., a compressor of an
air conditioning system, an electric fan).
[0085] Thereafter, when it is determined that the value of
difference between the upper limit inflow EGR gas quantity and the
cylinder-inflow EGR gas quantity is equal to or larger than the
threshold value at step 104, the operation proceeds to step 108. At
step 108, the misfire-avoidance control routine, i.e., the
misfire-avoidance control process is terminated (in a case where a
torque correcting control routine for executing at least one of the
above-discussed torque correcting control operations is executed,
the torque correcting control routine, i.e., the torque correcting
control process is also terminated).
[0086] Next, the estimating method for estimating the
cylinder-inflow EGR gas quantity executed by the cylinder-inflow
EGR gas quantity determining arrangement 36a of the ECU 36 will be
described in detail with reference to FIGS. 3 to 6.
[0087] As in the present embodiment, in the system that has the LPL
EGR device 28, which recirculates the EGR gas to the portion of the
intake conduit 12 located on the upstream side of the compressor 19
(the intake passage on the upstream side of the throttle valve 21),
the ECU 36 computes (estimates) the cylinder-inflow EGR gas
quantity as follows.
[0088] As shown in FIG. 6, a total cylinder-inflow gas quantity
computing portion 37 of the cylinder-inflow EGR gas quantity
determining arrangement 36a of the ECU 36 computes a total
throttle-passing gas flow quantity (a total quantity of gas that
passes through the throttle valve 21) by using a throttle model 39.
The throttle model 39 is a model that simulates the behavior of the
gas in the intake conduit 12 at the time of passing through the
throttle valve 21. For instance, a throttle model, which is recited
in JP2008-101626A, may be used as the throttle model 39.
[0089] Here, it should be noted that the computed value of the
total throttle-passing gas flow quantity (the total
throttle-passing gas flow quantity computed by using the throttle
model 39) may be corrected by using a fresh air flow quantity (a
flow quantity of the fresh air that flows through the intake
conduit 12), which is sensed with the air flow meter 14.
Specifically, in a state where a predetermined correction value
learning condition is satisfied (e.g., in a steady operational
state), a difference between the fresh air flow quantity, which is
sensed with the air flow meter 14, and the computed value of the
total throttle-passing gas flow quantity, is computed as a gas flow
quantity correction value, and this gas flow quantity correction
value is stored in the memory of the ECU 36. Then, the computed
value of the total throttle-passing gas flow quantity is corrected
by using the gas flow quantity correction value. In this way, the
total throttle-passing gas flow quantity can be accurately
obtained.
[0090] Further alternatively, in a case of a system, which does not
have the air flow meter 14, the fresh air flow quantity may be
estimated (computed) based on an intake conduit pressure, which is
sensed with an intake conduit pressure sensor (not shown). Then,
the computed value of the total throttle-passing gas flow quantity
may be corrected by using the estimated fresh air quantity.
Specifically, in the state where the predetermined correction value
learning condition is satisfied (e.g., in the steady operational
state), the fresh air flow quantity is estimated (computed) based
on the intake conduit pressure, which is sensed with the intake
conduit pressure sensor, by using a map or a mathematical equation.
Furthermore, the correction value of the fresh air flow quantity is
computed based on an air-fuel ratio feedback correction quantity by
using a map or a mathematical equation, and the estimated fresh air
flow quantity, which is estimated based on the intake conduit
pressure, is corrected by using the correction value. Thereafter, a
difference between the estimated fresh air flow quantity (the fresh
air flow quantity after the correction), which is estimated based
on the intake conduit pressure, and the computed value of the total
throttle-passing gas flow quantity is computed as a gas flow
quantity correction value, and this gas flow quantity correction
value is stored in the memory of the ECU 36. Then, the computed
value of the total throttle-passing gas flow quantity is corrected
by using the gas flow quantity correction value. In this way, even
in the case of the system, which does not have the air flow meter
14, the total throttle-passing gas flow quantity can be accurately
obtained.
[0091] Thereafter, an intake manifold pressure (a pressure in the
intake passage on the downstream side of the throttle valve 21) is
computed based on the total throttle-passing gas flow quantity and
a previous value of the total cylinder-inflow gas quantity by using
an intake manifold model 40. The intake manifold model 40 is a
model that simulates the behavior of the gas at the time of being
charged into a portion (e.g., the surge tank 23 and the intake
manifold 24) of the intake passage located on the downstream side
of the throttle valve 21 after passing through the throttle valve
21. For instance, an intake conduit model, which is recited in
JP2008-101626A, may be used as the intake manifold model 40.
[0092] Thereafter, the total cylinder-inflow gas quantity
(=cylinder-inflow fresh air quantity+cylinder-inflow EGR gas
quantity) is computed based on the intake manifold pressure by
using an intake valve model 41. The intake valve model 41 is a
model that simulates the behavior of the gas at the time of being
drawn into the cylinder after being charged into the portion of the
intake passage located on the downstream side of the throttle valve
21. An intake valve model, which is recited in JP2008-101626A, may
be used as the intake valve model 41.
[0093] A cylinder-inflow EGR gas flow quantity computing portion 38
of the cylinder-inflow EGR gas quantity determining arrangement 36a
of the ECU 36 computes an EGR valve-passing gas flow quantity (a
flow quantity of the EGR gas, which passes through the EGR valve
31) by using an EGR valve model 42. The EGR valve model 42 is a
model that simulates the behavior of the EGR gas at the time of
passing through the EGR valve 31 in the EGR conduit 29.
[0094] As shown in FIG. 7, the EGR valve model 42 is constructed as
a map that defines a relationship among the opening degree of the
EGR valve 31, the total throttle-passing gas flow quantity and the
EGR valve-passing gas flow quantity. The EGR valve-passing gas flow
quantity is computed based on the opening degree of the EGR valve
31 and the total throttle-passing gas flow quantity by using the
map of the EGR valve-passing gas flow quantity. The map of the EGR
valve-passing gas flow quantity is prepared in advance based on
test data and design data and is prestored in the ROM of the ECU
36.
[0095] Alternatively, the EGR valve model 42 may be constructed as
a mathematical or physics equation, which defines a relationship
among the opening degree of the EGR valve 31, a pressure Pin on the
upstream side of the EGR valve 31, a pressure Pout on the
downstream side of the EGR valve 31 and the EGR valve-passing gas
flow quantity Megr.
[0096] Specifically, the EGR valve model 42 may be approximated by
using the following equation of a throttle (equation of an
orifice).
Megr = C A Pin R Tegr .PHI. ( Pout / Pin ) ##EQU00001##
[0097] In the above equation, C denotes a discharge coefficient,
and A denotes an opening cross-sectional area of the EGR conduit
29, which changes in response to the opening degree of the EGR
valve 31. Furthermore, R denotes a gas constant, and Tegr denotes a
temperature of the EGR gas on the upstream side of the EGR valve
31. Furthermore, .PHI.(Pout/Pin) is a function that uses (Pout/Pin)
as a variable.
[0098] In this case, the EGR valve-passing gas flow quantity Megr
is computed based on the opening degree of the EGR valve 31, the
pressure Pin on the upstream side of the EGR valve 31, the pressure
Pout on the downstream side of the EGR valve 31, and the
temperature of the EGR gas by using the equation of the throttle
(the equation of the orifice) discussed above.
[0099] Thereafter, the cylinder-inflow EGR gas quantity is computed
based on the computed value of the EGR valve-passing gas flow
quantity by using an EGR gas delay model 43 (see FIG. 6). The EGR
gas delay model 43 is a model that simulates the behavior of the
EGR gas until the time of flowing into the cylinder by passing
through the throttle valve 21 after passing through the EGR valve
31.
[0100] As shown in FIG. 8, the EGR gas delay model 43 includes a
fresh air merging delay model 44, an intake conduit advection delay
model 45, an intake manifold charge delay model 46 and an intake
port advection delay model 47. The fresh air merging delay model 44
is a model that simulates the behavior of the EGR gas at the time
of flowing into a portion (a portion of the intake conduit 12
located on the upstream side of the compressor 19) of the intake
passage located on the upstream side of the throttle valve 21 after
passing through the EGR valve 31. The intake conduit advection
delay model 45 is a model that simulates the behavior of the EGR
gas until the time of passing through the throttle valve 21 after
flowing into the portion of the intake passage located on the
upstream side of the throttle valve 21. The intake manifold charge
delay model 46 is a model that simulates the behavior of the EGR
gas at the time of being charged into a portion (e.g., the surge
tank 23 and the intake manifold 24) of the intake passage located
on the downstream side of the throttle valve 21 after passing
through the throttle valve 21. The intake port advection delay
model 47 is a model that simulates the behavior of the EGR gas
until the time of flowing into the cylinder through the intake port
after being charged into the portion of the intake passage located
on the downstream side of the throttle valve 21.
[0101] Thereby, the delay of the EGR gas that occurs at the time of
flowing into the portion of the intake passage located on the
upstream side of the throttle valve 21, the convection delay of the
EGR gas that occurs until the time of passing through the throttle
valve 21 after flowing into the portion of the intake passage
located on the upstream side of the throttle valve 21, the charge
delay of the EGR gas that occurs at the time of being charged into
the portion of the intake passage located on the downstream side of
the throttle valve 21 after passing through the throttle valve 21,
and the convection delay of the EGR gas that occurs until the time
of flowing into the cylinder through the intake port after being
charged into the portion of the intake passage located on the
downstream side of the throttle valve 21 can be reflected into the
computation of the cylinder-inflow EGR gas quantity. Thus, the
estimation accuracy of the cylinder-inflow EGR gas quantity can be
improved.
[0102] At the time of computing the cylinder-inflow EGR gas
quantity, an EGR gas flow quantity Megr(b), which is a flow
quantity of the EGR gas that flows into the portion of the intake
passage located on the upstream side of the throttle valve 21, is
computed based on an EGR valve-passing gas flow quantity Megr(a) by
using the fresh air merging delay model 44.
[0103] The fresh air merging delay model is approximated by using
the following equation (1).
Megr(b)=[K1/(.tau.1+1)].times.Megr(a) Equation (1)
[0104] A coefficient K1 and the time constant .tau.1 of the above
equation (1) are values that are determined based on a conduit
diameter and a conduit length of the portion of the EGR conduit 29
(the portion of the EGR conduit 29 from the EGR valve 31 to a
merging portion, at which the EGR conduit 29 is connected to the
intake conduit 12) and the conduit diameter of the intake conduit
12. The coefficient K1 and the time constant .tau.1 are computed in
advance based on the test data and the design data.
[0105] Thereafter, an EGR gas flow quantity Megr(c), which is a
flow quantity of the EGR gas that passes through the throttle valve
21, is computed based on the EGR gas flow quantity Megr(b), which
is the flow quantity of the EGR gas that flows into the portion of
the intake passage located on the upstream side of the throttle
valve 21, and the total throttle-passing gas flow quantity Mth by
using the intake conduit advection delay model 45.
[0106] With reference to FIG. 9, the intake conduit advection delay
model 45 is constructed as follows. Specifically, the behavior of
the EGR gas of the continuous time system, which is measured until
the time of passing through the throttle valve 21 after flowing
into the portion of the intake passage located on the upstream side
of the throttle valve 21, is transformed into a plurality of
matrices, which are formed at predetermined time intervals through
the discretization (e.g., 32 matrices, which are formed one after
another at 16 millisecond sampling time intervals through the
discretization). These matrices construct the intake conduit
advection delay model 45 and form a queue, i.e., the first in first
out (FIFO) data structure in the memory (rewritable memory or
storage) of the ECU 36. Each matrix indicates the corresponding EGR
gas flow quantity. In general, a moving speed of the EGR gas in the
intake conduit 12 is sufficiently slow in comparison to the
computation speed of the ECU 36, so that the intake conduit
advection delay model 45 can be constructed by the matrices, which
are formed one after another at the predetermined time intervals
through the discretization. Various coefficients, which are used in
the intake conduit advection delay model 45, are values that are
determined based on a conduit diameter and a conduit length of a
portion of the intake conduit 12 (the portion of the intake conduit
12 that is from the merging portion, at which the EGR conduit 29 is
connected to the intake conduit 12, to the throttle valve 21) and
are computed in advance based on the test data and the design
data.
[0107] Thereafter, as shown in FIG. 8, the intake manifold charge
delay model 46 is used to compute an EGR gas flow quantity Megr(d),
which is a flow quantity of the EGR gas charged into the portion
(e.g., the surge tank 23 and the intake manifold 24) of the intake
passage located on the downstream side of the throttle valve 21,
based on the EGR gas flow quantity Megr(c), which is the flow
quantity of the EGR gas that passes through the throttle valve
21.
[0108] The intake manifold charge delay model 46 is approximated by
using the following equation (2).
Megr(d)=[K2/(.tau.2+1)].times.Megr(c) Equation (2)
[0109] A coefficient K2 and an intake manifold charge delay time
constant .tau.2 of the above equation (2) are values that are
determined based on, for example, a conduit diameter, a length and
a volume of the portion (the portion, such as the surge tank 23 and
the intake manifold 24, of the intake conduit 12 located on the
downstream side of the throttle valve 21) of the intake passage
located on the downstream side of the throttle valve 21. The
coefficient K2 and the intake manifold charge delay time constant
.tau.2 of the above equation (2) are computed in advance based on
the test data and the design data. In a case where the intake
manifold charge delay time constant is used in the intake manifold
model 40, the intake manifold charge delay time constant, which is
used in the intake manifold model 40, may be used in the intake
manifold charge delay model 46.
[0110] Thereafter, the intake port advection delay model 47 is used
to compute a cylinder-inflow EGR gas quantity Megr(e) based on the
EGR gas flow quantity Megr(d), which is the flow quantity of the
EGR gas charged into the portion of the intake passage located on
the downstream side of the throttle valve 21, and the previous
value of the total cylinder-inflow gas quantity.
[0111] The intake port advection delay model 47 is constructed as
follows. Specifically, the behavior of the EGR gas of the
continuous time system, which is measured until the time of flowing
into the cylinder through the intake port after being charged into
the portion of the intake passage located on the downstream side of
the throttle valve 21, is transformed into a plurality of matrices,
which are formed one after another at predetermined time intervals
through discretization. These matrices construct the intake port
advection delay model 47 and form a queue, i.e., the first in first
out (FIFO) data structure in the memory of the ECU 36. Various
coefficients, which are used in the intake port advection delay
model 47, are values that are determined based on the conduit
diameter and the conduit length of the corresponding portion of the
intake conduit 12 and are computed in advance based on the test
data and the design data.
[0112] Now, an advantage of the present embodiment will be
described in comparison to first and second comparative examples
(previously proposed techniques) with reference to FIGS. 10A to
10D. FIG. 10A is a diagram showing a change in a throttle opening
degree (an opening degree of the throttle valve 21) with time. More
specifically, during the time of decelerating the engine (see a
period of "DECEL." in FIG. 10A), the throttle opening degree is
reduced. Thereafter, during the time of reaccelerating the engine
(see a period of "ACCEL." in FIG. 10A), the throttle opening degree
is increased. FIG. 10B shows a change in the cylinder-inflow EGR
gas quantity and a change in the upper limit inflow EGR gas
quantity with time in the first comparative example. FIG. 10C shows
a change in the cylinder-inflow EGR gas quantity and a change in
the upper limit inflow EGR gas quantity with time in the second
comparative example. FIG. 10D shows a change in the cylinder-inflow
EGR gas quantity and a change in the upper limit inflow EGR gas
quantity with time in the present embodiment. In the system of the
first comparative example shown in FIG. 10B, which does not execute
any misfire-avoidance control operation, when the throttle opening
degree is controlled to the closing side during the time of
decelerating the engine (see the period of "DECEL." in FIG. 10B),
the intake air quantity is decreased, and thereby the upper limit
inflow EGR gas quantity is decreased. Furthermore, since the EGR
gas remains in the intake passage at this time, the cylinder-inflow
EGR gas quantity may possibly exceed the upper limit inflow EGR gas
quantity at the time of decelerating the engine and/or at the time
of reaccelerating the engine (see the period of "ACCEL" in FIG.
10B), thereby possibly causing the misfire.
[0113] In the system of the second comparative example shown in
FIG. 10C, a combustion deterioration limiting control operation is
executed such that the throttle opening degree is reduced at a
speed that is lower than an upper limit closing speed at the time
of decelerating the engine (see the period of "DECEL." in FIG.
10C). The upper limit closing speed is an upper limit of the
closing speed of the throttle valve 21, equal to or below which the
normal combustion (combustion without misfire) is possible. In FIG.
10C, a dotted line is shown for illustrative purpose to indicate
the upper limit inflow EGR gas quantity of the system of FIG. 10B,
in which no misfire-avoidance control operation is executed. In the
system of the second comparative example shown in FIG. 10C, the
combustion deterioration limiting control operation may be
excessively executed in an initial decelerating range (an initial
range of the deceleration operation of the engine), in which the
cylinder-inflow EGR gas quantity is equal to or below the upper
limit inflow EGR gas quantity, so that the fuel consumption may
possibly be deteriorated. Furthermore, even when the combustion
deterioration limiting control operation is executed, the
cylinder-inflow EGR gas quantity may possibly exceed the upper
limit inflow EGR gas quantity thereafter, thereby possibly
resulting in the generation of the misfire, as indicated by a
shaded area (a misfire generating range) in FIG. 10C. Furthermore,
the system of the second comparative example shown in FIG. 10C
cannot counteract with the case where the EGR gas remains in the
intake passage until the time of reaccelerating the engine after
the execution of the deceleration of the engine, thereby possibly
resulting in the occurrence of the misfire at the time of
reacceleration of the engine (see the beginning of the period of
"ACCEL" in FIG. 10C).
[0114] Unlike the first and second comparative examples discussed
above, according to the present embodiment, with reference to FIG.
10D, the cylinder-inflow EGR gas quantity is estimated by using the
model, which simulates the behavior of the EGR gas flow quantity,
and it is predicted whether the misfire occurs based on the result
of the determination of whether the value of the difference between
the currently set upper limit inflow EGR gas quantity and the
estimated cylinder-inflow EGR gas quantity is smaller than the
predetermined threshold value. When it is predicted that the
misfire occurs (i.e., when it is predicted that the event of
misfire is upcoming), the misfire-avoidance control
operation(s)(e.g., the fuel injection quantity increasing control
operation, the ignition energy increasing control operation, and/or
the gas flow strengthening control operation, the intake air
quantity increasing control operation) is executed. Thereby, when
it is predicted that the misfire occurs in view of the excessive
increase of the cylinder-inflow EGR gas quantity, the
misfire-avoidance control operation(s) is executed. Therefore, the
occurrence of the misfire caused by the EGR gas at the time of the
decelerating the engine and the time of reaccelerating the engine
can be limited. In FIG. 10D, a lower dotted line indicates the
upper limit inflow EGR gas quantity of the first comparative
example, and an upper dotted line indicates the upper limit inflow
EGR gas quantity of the second comparative example.
[0115] Furthermore, in the present embodiment, the required
increase of the upper limit inflow EGR gas quantity is computed
based on the difference between the cylinder-inflow EGR gas
quantity and the upper limit inflow EGR gas quantity, and the
misfire-avoidance control operation(s) is executed under the
condition, which corresponds to the required increase of the upper
limit inflow EGR gas quantity. Therefore, the condition of
executing the misfire-avoidance control operation(s) (e.g., the
type of the misfire-avoidance control operation(s), the combination
of the misfire-avoidance control operation(s), the control quantity
of the misfire-avoidance control operation(s), and/or the execution
timing of the misfire-avoidance control operation(s)) can be
changed according to the required increase of the upper limit
inflow EGR gas quantity, so that the misfire-avoidance control
operation(s) can be executed under the condition, which is suitable
for achieving the required increase of the upper limit inflow EGR
gas quantity.
[0116] Furthermore, in the present embodiment, the
misfire-avoidance control operation(s) to be executed at the
present time is selected from the various types of the
misfire-avoidance control operations in view of the influence on
the fuel economy, the influence on the driveability, the influence
on the emission and the influence on the engine responsiveness of
the misfire-avoidance control operation(s). Therefore, it is
possible to limit the deterioration of the fuel economy, the
deterioration of the driveability and the deterioration of the
emission as well as the delay of the engine response upon the
execution of the misfire-avoidance control operation(s).
[0117] In the above embodiment, the cylinder-inflow EGR gas
quantity is computed (estimated) by using the model, which
simulates the behavior of the EGR gas flow quantity. However, the
method of estimating the cylinder-inflow EGR gas quantity is not
limited to this method and may be modified in an appropriate
manner. For example, the cylinder-inflow EGR gas quantity may be
computed (estimated) based on an output signal of an intake conduit
pressure sensor or an output signal of the air flow meter.
Furthermore, the quantity of the EGR gas, which remains in the
intake conduit 12, may be sensed with a sensor as information of
the cylinder-inflow EGR gas quantity (cylinder-inflow EGR gas
quantity information).
[0118] In the above embodiment, the required increase of the upper
limit inflow EGR gas quantity is computed based on the difference
between the cylinder-inflow EGR gas quantity and the upper limit
inflow EGR gas quantity. However, the present disclosure is not
limited to this. For instance, in view of the fact of that the
upper limit inflow EGR gas quantity changes in response to the
engine operational state (e.g., the intake air quantity), the
required increase of the upper limit inflow EGR gas quantity may be
computed based on the cylinder-inflow EGR gas quantity and the
engine operational state.
[0119] In the above embodiment, the present disclosure is applied
to the engine that is provided with the supercharger and the low
pressure loop (LPL) EGR device 28, which recirculates the EGR gas
from the portion of the exhaust conduit 15 located on the
downstream side of the catalytic converter 16 to the portion of the
intake conduit 12 located on the upstream side of the compressor
19. However, the present disclosure is not limited to such an
engine. For example, the present disclosure may be applied to an
internal combustion engine that is provided with a super charger
and a high pressure loop (HPL) EGR device, which recirculates the
EGR gas from a portion of the exhaust conduit located on an
upstream side of the exhaust turbine to a portion of the intake
conduit located on a downstream side of the throttle valve.
[0120] Furthermore, the present disclosure is not limited to the
engine, which is provided with the exhaust turbine supercharger
(i.e., the turbocharger). For instance, the present disclosure may
be applied to an internal combustion engine, which is provided with
a mechanical supercharger or an electric supercharger.
[0121] Furthermore, the present disclosure is not limited to the
engine, which is provided with the supercharger. That is, the
present disclosure may be applied to a normal aspiration engine (NA
engine), which is not provided with a supercharger.
[0122] Additional advantages and modifications will readily occur
to those skilled in the art. The present disclosure in its broader
terms is therefore not limited to the specific details,
representative apparatus, and illustrative examples shown and
described.
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